/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.tomcat.util.http.fileupload;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.List;

/**
 * This class implements an output stream in which the data is
 * written into a byte array. The buffer automatically grows as data
 * is written to it.
 * <p>
 * The data can be retrieved using <code>toByteArray()</code> and
 * <code>toString()</code>.
 * <p>
 * Closing a <tt>ByteArrayOutputStream</tt> has no effect. The methods in
 * this class can be called after the stream has been closed without
 * generating an <tt>IOException</tt>.
 * <p>
 * This is an alternative implementation of the {@link java.io.ByteArrayOutputStream}
 * class. The original implementation only allocates 32 bytes at the beginning.
 * As this class is designed for heavy duty it starts at 1024 bytes. In contrast
 * to the original it doesn't reallocate the whole memory block but allocates
 * additional buffers. This way no buffers need to be garbage collected and
 * the contents don't have to be copied to the new buffer. This class is
 * designed to behave exactly like the original. The only exception is the
 * deprecated toString(int) method that has been ignored.
 */
public class ByteArrayOutputStream extends OutputStream {

	/**
	 * A singleton empty byte array.
	 */
	private static final byte[] EMPTY_BYTE_ARRAY = new byte[0];

	/**
	 * The list of buffers, which grows and never reduces.
	 */
	private final List<byte[]> buffers = new ArrayList<byte[]>();
	/**
	 * The index of the current buffer.
	 */
	private int currentBufferIndex;
	/**
	 * The total count of bytes in all the filled buffers.
	 */
	private int filledBufferSum;
	/**
	 * The current buffer.
	 */
	private byte[] currentBuffer;
	/**
	 * The total count of bytes written.
	 */
	private int count;

	/**
	 * Creates a new byte array output stream. The buffer capacity is
	 * initially 1024 bytes, though its size increases if necessary.
	 */
	public ByteArrayOutputStream() {
		this(1024);
	}

	/**
	 * Creates a new byte array output stream, with a buffer capacity of
	 * the specified size, in bytes.
	 *
	 * @param size the initial size
	 * @throws IllegalArgumentException if size is negative
	 */
	public ByteArrayOutputStream(int size) {
		if (size < 0) {
			throw new IllegalArgumentException(
					"Negative initial size: " + size);
		}
		synchronized (this) {
			needNewBuffer(size);
		}
	}

	/**
	 * Makes a new buffer available either by allocating
	 * a new one or re-cycling an existing one.
	 *
	 * @param newcount the size of the buffer if one is created
	 */
	private void needNewBuffer(int newcount) {
		if (currentBufferIndex < buffers.size() - 1) {
			//Recycling old buffer
			filledBufferSum += currentBuffer.length;

			currentBufferIndex++;
			currentBuffer = buffers.get(currentBufferIndex);
		} else {
			//Creating new buffer
			int newBufferSize;
			if (currentBuffer == null) {
				newBufferSize = newcount;
				filledBufferSum = 0;
			} else {
				newBufferSize = Math.max(
						currentBuffer.length << 1,
						newcount - filledBufferSum);
				filledBufferSum += currentBuffer.length;
			}

			currentBufferIndex++;
			currentBuffer = new byte[newBufferSize];
			buffers.add(currentBuffer);
		}
	}

	/**
	 * Write the bytes to byte array.
	 *
	 * @param b   the bytes to write
	 * @param off The start offset
	 * @param len The number of bytes to write
	 */
	@Override
	public void write(byte[] b, int off, int len) {
		if ((off < 0)
				|| (off > b.length)
				|| (len < 0)
				|| ((off + len) > b.length)
				|| ((off + len) < 0)) {
			throw new IndexOutOfBoundsException();
		} else if (len == 0) {
			return;
		}
		synchronized (this) {
			int newcount = count + len;
			int remaining = len;
			int inBufferPos = count - filledBufferSum;
			while (remaining > 0) {
				int part = Math.min(remaining, currentBuffer.length - inBufferPos);
				System.arraycopy(b, off + len - remaining, currentBuffer, inBufferPos, part);
				remaining -= part;
				if (remaining > 0) {
					needNewBuffer(newcount);
					inBufferPos = 0;
				}
			}
			count = newcount;
		}
	}

	/**
	 * Write a byte to byte array.
	 *
	 * @param b the byte to write
	 */
	@Override
	public synchronized void write(int b) {
		int inBufferPos = count - filledBufferSum;
		if (inBufferPos == currentBuffer.length) {
			needNewBuffer(count + 1);
			inBufferPos = 0;
		}
		currentBuffer[inBufferPos] = (byte) b;
		count++;
	}

	/**
	 * Writes the entire contents of the specified input stream to this
	 * byte stream. Bytes from the input stream are read directly into the
	 * internal buffers of this streams.
	 *
	 * @param in the input stream to read from
	 * @return total number of bytes read from the input stream
	 * (and written to this stream)
	 * @throws IOException if an I/O error occurs while reading the input stream
	 * @since 1.4
	 */
	public synchronized int write(InputStream in) throws IOException {
		int readCount = 0;
		int inBufferPos = count - filledBufferSum;
		int n = in.read(currentBuffer, inBufferPos, currentBuffer.length - inBufferPos);
		while (n != -1) {
			readCount += n;
			inBufferPos += n;
			count += n;
			if (inBufferPos == currentBuffer.length) {
				needNewBuffer(currentBuffer.length);
				inBufferPos = 0;
			}
			n = in.read(currentBuffer, inBufferPos, currentBuffer.length - inBufferPos);
		}
		return readCount;
	}

	/**
	 * Closing a <tt>ByteArrayOutputStream</tt> has no effect. The methods in
	 * this class can be called after the stream has been closed without
	 * generating an <tt>IOException</tt>.
	 *
	 * @throws IOException never (this method should not declare this exception
	 *                     but it has to now due to backwards compatability)
	 */
	@Override
	public void close() throws IOException {
		//nop
	}

	/**
	 * Writes the entire contents of this byte stream to the
	 * specified output stream.
	 *
	 * @param out the output stream to write to
	 * @throws IOException if an I/O error occurs, such as if the stream is closed
	 * @see java.io.ByteArrayOutputStream#writeTo(OutputStream)
	 */
	public synchronized void writeTo(OutputStream out) throws IOException {
		int remaining = count;
		for (byte[] buf : buffers) {
			int c = Math.min(buf.length, remaining);
			out.write(buf, 0, c);
			remaining -= c;
			if (remaining == 0) {
				break;
			}
		}
	}

	/**
	 * Gets the curent contents of this byte stream as a byte array.
	 * The result is independent of this stream.
	 *
	 * @return the current contents of this output stream, as a byte array
	 * @see java.io.ByteArrayOutputStream#toByteArray()
	 */
	public synchronized byte[] toByteArray() {
		int remaining = count;
		if (remaining == 0) {
			return EMPTY_BYTE_ARRAY;
		}
		byte newbuf[] = new byte[remaining];
		int pos = 0;
		for (byte[] buf : buffers) {
			int c = Math.min(buf.length, remaining);
			System.arraycopy(buf, 0, newbuf, pos, c);
			pos += c;
			remaining -= c;
			if (remaining == 0) {
				break;
			}
		}
		return newbuf;
	}

	/**
	 * Gets the curent contents of this byte stream as a string.
	 *
	 * @return the contents of the byte array as a String
	 * @see java.io.ByteArrayOutputStream#toString()
	 */
	@Override
	public String toString() {
		return new String(toByteArray());
	}
}
